﻿292 



BR. STANLEY SMITH ON AVLIXA HO II FOR MIS, [vol. lxxii, 



characters above mentioned, and the tube appears as a polygonal 

 ring. The number of septa in each cycle is usually eleven ; very 



rarely does it exceed 

 twelve or is it less 

 than ten. The theca 

 is emphasized by a 

 very slight secondary 

 thickening of the dis- 

 sepiments which form 

 it. The diameter of 

 the theca is about 1*5 

 mm., and the diameter 

 of the tube about 0*5 

 mm. The dilation of 

 the septa at the theca 

 does not extend far in 

 a peripheral direction 

 (as indicated in the 

 figure). 



Longitudinal 



section (PI. XXII, fig. 8). — The tube is represented by two 

 vertical walls limiting the horizontal tabula? ; the tabulae external 

 to these Avails are seen as inclined plates. 



Ontogeny. 



In the earliest growth-stages observed in Aulina the septa then 

 present meet in the centre of the corallites (PI. XXII, figs. 9-11). 

 Later, these leave the centre and form the initial stage of the tube, 

 while new members are being added to their number. 



Although, by the time that it reaches the adult stage, the form 

 displays a radial symmetry, the insertion of septa follows the 

 general rule appertaining to the Rugosa as a class. A cardinal 

 fossula (in some cases very conspicuously, but in others less pro- 

 minently displayed) and a distinct pinnate symmetry may be 

 observed in the immature stage. 



Phylogeny. 



The morphology of Aulina clearly points to its derivation from 

 PTiiUipsastrcea : the axial tube in the former and the dilated 

 edges of the septa in the latter are probable stages in a continuous 

 line of development. The interval of time, however, separating 

 the epochs in which the two genera lived respectively is consider- 

 able — practically the whole of the Lower Carboniferous Period, 

 and no intermediate forms have as yet been recorded from the 

 beds of that age. 



Horizon and locality. — Aulina occurs abundantly in the 

 Pell Top Limestone in the vicinity of Harlow Hill, 1 where the 



1 Harlow Hill lies on the Newcastle and Carlisle Road, 11 miles west of the 

 former city (Quarter Sheet 105 N.W. New Series 14). 



Fig. 4. — Diagram combining a transverse 

 and a longitudinal section of Aulina 

 rotiformis. x about 18 diameters. 



